CN109705337B

CN109705337B - Continuous synthesis method of polyamide and vertical multi-stage reactor

Info

Publication number: CN109705337B
Application number: CN201910063549.8A
Authority: CN
Inventors: 刘天奇; 王嘉骏; 顾雪萍; 冯连芳
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2019-01-23
Filing date: 2019-01-23
Publication date: 2020-04-10
Anticipated expiration: 2039-01-23
Also published as: CN109705337A

Abstract

The invention provides a continuous synthesis method of polyamide, which synthesizes polyamide by means of gas-liquid parallel flow and gas-phase pressure gradual decrease, avoids the escape of a large amount of diamine and water at the early stage of reaction, and ensures the complete reaction of polyamide salt; in the later stage of the reaction, the gas phase pressure is low, which is beneficial to removing water in the reaction system and promoting the increase of the molecular weight of the polyamide, the polymerization degree of the product reaches 20-60, and the requirement of a subsequent pressure reducing device is reduced or eliminated. The invention further provides a reactor for implementing the method, which is beneficial to increasing the reliability of the reaction process, reducing the energy requirement, reducing the investment and maintenance expenditure of equipment and the like.

Description

Continuous synthesis method of polyamide and vertical multi-stage reactor

Technical Field

The present invention relates to a continuous polymerization process for producing polyamides and to an apparatus for carrying out the polymerization process. More precisely, the invention relates to a continuous synthesis process and a vertical multistage reactor for polyamides.

Background

Methods for the continuous preparation of polyamide materials such as nylon 66 are known in the art and conventional production schemes involve the use of 3 to 5 different reaction vessels connected in series. These processes for the production of polyamide materials require a plurality of reaction steps, which are usually carried out in tubular reactors or stirred tanks, and which mainly comprise the processes of evaporative concentration, high-pressure prepolycondensation, flash evaporation, atmospheric finishing and vacuum polycondensation, and which are carried out spatially separately from one another. Page 52 of "basic knowledge of nylon 66 production" published by the publication of the textile industry of China introduces the continuous production process of nylon 66 introduced from French Rona-Planck by the Liaoyang petrochemical industry of China, and the main links comprise concentration, high-pressure pre-polycondensation, flash evaporation and normal-pressure polycondensation; page 76 of the book introduces a nylon 66 continuous polymerization device process introduced by the shenma group of china from asahi formation, the main links include concentration, high-pressure pre-polycondensation, flash evaporation, normal-pressure polycondensation and vacuum polycondensation; the US patent US3402152 discloses a continuous polymerization plant process for nylon 66 invented by monsanto corporation, the main links include concentration, high pressure pre-polycondensation, flash evaporation, normal pressure polycondensation, vacuum polycondensation. The above flow is the mainstream of the current nylon 66 continuous polymerization flow, and has the following disadvantages: 1. the process is long, and the construction investment and operation cost is high; 2. the tubular reactor is adopted in the high-pressure pre-polycondensation stage, the whole reaction process keeps higher pressure, the evaporation of water which is a reaction product is not facilitated, and the increase of the molecular weight of the polyamide is limited in chemical balance; 3. the pressure in the flash evaporation process is suddenly reduced from more than 15atm to normal pressure, long reaction time is needed, the material viscosity in the process is high, condensed water is not easy to evaporate, and the increase of the molecular weight of the polyamide is restricted; 4. the polyamide brought out along with the condensed water evaporation clamp in the flash evaporation process and the fluctuation of the reaction liquid level easily cause the scabbing of the reactor wall, and the subsequent cleaning is troublesome.

In order to overcome the disadvantages of the conventional continuous production scheme for polyamides, a novel integrated reaction apparatus suitable for the continuous production of polyamide materials is disclosed. U.S. Pat. No. 3,3296217 discloses a falling tube and rectifying tray integrated tower reactor invented by Monsanto; chinese patent CN105745250A discloses a multistage reactor for gas-liquid reverse running of monomer feed with unequal stoichiometric numbers invented by westert technologies; chinese patent CN201210254788.X discloses a gas-liquid converse integrated tower type reaction equipment which uses binary monomer as raw material and contains rectification section and falling film reaction section. The disclosed novel integrated reaction device improves the defects of the traditional polyamide process to a certain extent, simplifies the reaction process and improves the reaction efficiency. However, in order to ensure that the liquid phase flows from the top of the tower to the bottom of the tower, the gas phase moves reversely from the bottom of the tower to contact with the liquid phase, and the pressure of the whole tower is gradually increased from top to bottom, so that the following defects exist: 1. the pressure at the liquid phase inlet is low, a large amount of water is evaporated, and the heat load is increased rapidly to keep the temperature required by the reaction; 2. the lower pressure in the upper part of the reactor causes a large amount of diamine to evaporate, which can affect the condensation reaction; 3. the rapid concentration of the liquid phase in the upper part of the reactor risks the precipitation of unreacted polyamide salts; 4. the polyamide product flows out of the tower kettle at higher pressure, and still needs to be provided with a decompression device with longer residence time to enter a subsequent normal pressure or vacuum polycondensation reactor for reaction.

Disclosure of Invention

In view of these drawbacks of the prior art, it is an object of the present invention to provide a continuous process for the synthesis of polyamides and a vertical multistage reactor.

The technical scheme adopted by the invention is as follows: a continuous synthesis method of polyamide is characterized in that the method comprises the following steps: and (2) taking a solution containing polyamide salt water as a liquid phase stream, taking a gas containing inert gas, water vapor and diamine as a gas phase stream, and carrying out multistage reaction to synthesize the polyamide, wherein the flow directions of the liquid phase stream A and the gas phase stream B are the same, and the gas phase pressure of each stage of reaction is gradually reduced along the flow direction.

The polyamide salt is selected from self-lactam salt, undecaplactam salt, dodecalactam salt, butanediamine adipate, pentanediamine adipate, hexanediamine sebacate, hexanediamine dodecacarbonate, decanediamine sebacate and dodecadiamine dodecacarbonate.

Further, the gas phase pressure of the first-stage reaction is 20atm or less, and the gas phase pressure of the last reaction is 1atm or more. Preferably, the gas phase pressure of the first stage reaction is 18 atm.

A vertical multi-stage reactor comprises a plurality of reaction layers; the reactor has a liquid phase inlet and a gas phase inlet at the top and an outlet at the bottom.

Each reaction layer comprises an evaporator and a tubular pressure reduction unit, the evaporator comprises a groove body and a first tower tray positioned above the groove body, an outlet of the first tower tray is positioned above the groove body, and the groove body is provided with a heat supply coil pipe;

the tubular pressure reducing unit comprises a snake-shaped pressure reducing pipe and a second tray positioned above the snake-shaped pressure reducing pipe, an outlet of the second tray is connected with the snake-shaped pressure reducing pipe, and a heat exchange jacket is coated on the outer side of the snake-shaped pressure reducing pipe; the edges of the first tower tray and the second tower tray are hermetically connected with the wall of the reactor; the liquid phase material and the gas phase material first enter the trough through the outlet of the first tray. The liquid and gas overflowing from the groove body flow downwards from the gap between the groove body and the wall of the reactor, enter the serpentine pressure reducing pipe through the outlet of the second tray, and flow out from the outlet of the serpentine pressure reducing pipe to the first tray of the next reaction layer.

All the reaction layers except the first reaction layer are provided with gas phase outlets for discharging gas overflowing from the groove body;

the reaction layer is divided into a first-stage reaction layer and a second-stage reaction layer, the first-stage reaction layer is positioned above the second-stage reaction layer, wherein in each second-stage reaction layer, a liquid-phase inlet is arranged at the edge of the first tray, the gas discharged from the gas-phase outlet is separated to obtain diamine, and the diamine is input from the liquid-phase inlet and flows into the first tray of the next reaction layer together with the liquid and the gas flowing out from the outlet of the serpentine decompression pipe on the upper layer.

Furthermore, the number of the first stage reaction layers is 2-12, and the number of the second stage reaction layers is 2-12.

Further, the first tray has a funnel configuration with a slope angle from the edge to the outlet of no more than 15 degrees.

And the gas-liquid separation device comprises a plurality of immersed pipelines, the upper ends of the immersed pipelines are connected with the first tray, the lower ends of the immersed pipelines are inserted into the tank body, and the liquid-phase immersed pipelines in the center are inserted into liquid to a greater depth than the plurality of gas-phase immersed pipelines dispersed around. The gas-phase immersion pipelines are evenly distributed along the circumference of the liquid-phase immersion pipeline.

Further, the length of the gas-phase immersion lines towards the respective difference is uniform. Or arranged in a manner of alternating long and short lengths.

According to another aspect of the invention, there is provided a vertical multistage reactor suitable for carrying out the process of the invention, wherein the reactor comprises two reaction stages and internal features suitable for the parallel flow contact of the liquid phase stream a and the gaseous phase stream B in the two reaction stages and structural features of the horizontal tray at the injection of the reflux liquid phase stream C.

The invention has the beneficial effects that: the polyamide is synthesized by the way of gas-liquid parallel flow and gas-phase pressure gradual decrease, so that the escape of a large amount of diamine and water in the early stage of reaction is avoided, and the complete reaction of polyamide salt is ensured; in the later stage of the reaction, the gas phase pressure is low, which is beneficial to removing water in the reaction system and promoting the increase of the molecular weight of the polyamide, the polymerization degree of the product reaches 20-60, and the requirement of a subsequent pressure reducing device is reduced or eliminated. The invention further provides a reactor for implementing the method, which is beneficial to increasing the reliability of the reaction process, reducing the energy requirement, reducing the investment and maintenance expenditure of equipment and the like.

Drawings

FIG. 1 shows a front view of a vertical multistage reactor according to the invention;

FIG. 2 shows a tray configuration with vapor/liquid separation means in a multi-layer evaporator of the present invention;

FIGS. 3a and 3b show two variants of vapor/liquid separation devices in a multi-layer evaporator;

FIGS. 4a and 4b show two embodiments of a pressure reduction unit;

in the figure: liquid phase inlet 1, gas phase inlet 2, vapor outlet (3a, 3b, 3c), reflux diamine inlet (4a, 4b), outlet 5, tray (6a, 6b), trough 7, overflow weir 8, vapor/liquid separation device 9, evaporator 10, serpentine vacuum tube 11, collection trough 17, gas phase immersion line 18, liquid phase immersion line 19, serpentine vacuum tube inlet 22, heat exchange jacket 24.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

The invention provides a continuous synthesis method of polyamide, which comprises the following steps: and (2) taking a solution containing polyamide salt water as a liquid phase stream, taking a gas containing inert gas, water vapor and diamine as a gas phase stream, and carrying out multistage reaction to synthesize the polyamide, wherein the flow directions of the liquid phase stream A and the gas phase stream B are the same, and the gas phase pressure of each stage of reaction is gradually reduced along the flow direction. In the early stage of the reaction, the higher gas phase pressure can avoid the escape of a large amount of diamine and water, and the complete reaction of the polyamide salt is ensured; and in the later reaction stage, the gas phase pressure is low, so that water in a reaction system can be removed, and the increase of the molecular weight of the polyamide is promoted. The reaction mode of parallel flow and gradually decreased air pressure ensures that the polymerization degree of the product reaches 20-60, and effectively solves the contradiction between diamine volatilization and molecular weight increase.

Based on the above reaction modes, the present invention uses a multistage reactor as shown in fig. 1, which contains a plurality of reaction layers for implementing the above multistage reaction; the reactor has a liquid phase inlet 1 and a gas phase inlet 2 at the top and an outlet 5at the bottom. Wherein the liquid phase inlet 1 is used for injecting a liquid phase stream and the gas phase inlet 2 is used for injecting an inert gas. The water vapor and diamine in the vapor phase stream are both evaporation products of the liquid phase stream.

Each reaction layer comprises an evaporator 10 and a tubular pressure reduction unit, the evaporator 10 comprises a tank body 7 and a first tray 6a positioned above the tank body 7, the outlet of the first tray 6a is positioned above the tank body 7, and the tank body 7 is provided with a heat supply coil 20;

the tubular pressure reduction unit comprises a serpentine pressure reduction pipe 11 and a second tray 6b positioned above the serpentine pressure reduction pipe 11, an outlet of the second tray 6b is connected with the serpentine pressure reduction pipe 11, and a heat exchange jacket 24 is coated on the outer side of the serpentine pressure reduction pipe 11; the edges of the first tray 6a and the second tray 6b are hermetically connected with the wall of the reactor; the liquid-phase material and the gas-phase material first enter the tank 7 through the outlet of the first tray 6 a. The liquid and gas overflowing from the trough body 7 flow downward from the gap between the trough body 7 and the reactor wall, enter the serpentine-shaped pressure reducing pipe 11 through the outlet of the second tray 6b, and flow out from the outlet of the serpentine-shaped pressure reducing pipe 11 to the first tray 6a of the next reaction layer.

All the reaction layers except the first reaction layer are provided with steam outlets (3a, 3b, 3c) for discharging gas overflowed from the groove body 7, and the steam outlets can be provided with valves through which the amount of discharged steam is controlled, so that the reaction balance is regulated and controlled;

the reaction layer is divided into a first-stage reaction layer and a second-stage reaction layer, the first-stage reaction layer is positioned above the second-stage reaction layer, and as the gas phase pressure of the second stage is lower and the diamine volatilizes faster, reflux diamine inlets (4a, 4b) are arranged at the edge of the first tray in each second-stage reaction layer for injecting diamine, and the diamine can be input externally or obtained by separating gas discharged from the gas phase outlet; flows into the first tray 6a of the next reaction layer together with the liquid and gas flowing out from the outlet of the serpentine-shaped pressure reducing pipe 11 of the previous layer.

The polyamide salt solution is injected under pressure into the first reaction layer of the multistage reactor from the liquid phase inlet 1. Suitable polyamide salt solutions have a concentration of not less than 30 wt%, preferably at least 50 wt%. An inert gas is injected into the reactor headspace through the gas phase inlet 2 or no inert gas is injected. The liquid stream a containing polyamide brine is gradually collected to the center by gravity in the tray 6a inclined toward the center and enters the evaporator 10 in parallel with the vapor stream B containing inert gas and small molecule components vaporized from the liquid phase or only small molecule components vaporized from the liquid phase. Through the separation of the vapor/liquid separation device 9, the gas phase and the liquid phase respectively enter the interior of the vertical groove body 7 through different channels. As the reaction mass continues to be injected, stream B of liquid phase in the vertical trough overflows weir 8 around the peripheral edge and then flows towards inclined tray 6B. The gas phase B bubbling out of the liquid phase in the evaporator 10 also passes through the vertical trough and the annular space of the inner wall of the reactor into the gas phase space above the tray 6B. Under the action of gravity and of the gas phase pressure, the liquid phase stream a and the gas phase stream B are mixed again into the serpentine decompression tube 11. The gas-liquid mixture rapidly reduces the pressure through the tubular pressure reduction unit and continuously enters the subsequent repeated structural unit for condensation polymerization reaction. A liquid phase stream C mainly containing diamine, which is obtained by recovering a mixed vapor comprising the inert gas and water and diamine produced during the reaction or comprising only water and diamine produced during the reaction, discharged from the reactor, through a conventional separation device like a rectifying column, is returned to the reaction system through a plurality of reflux diamine inlets (4a, 4b) provided at the second stage to be replenished. The gas phase and the liquid phase in the multi-stage tower reactor flow in parallel in a whole, the reaction is carried out under the operation of reducing pressure step by step, and finally the reaction product is gathered in a polymer collecting tank 17 at the bottom of the reactor and qualified polymer product flows out from a polyamide material outlet 5.

Preferably, the number of the reaction layers in the first stage is 2-12, the number of the reaction layers in the second stage is 2-12, and the polymerization degree of the product can be effectively controlled by regulating and controlling the number of the reaction layers in the two stages so as to adapt to the production requirements of polyamide materials with different performances.

The first tray 6a has a funnel structure with an inclination angle from the edge to the outlet of not more than 15 degrees.

Fig. 2 shows a tray configuration with vapor/liquid separation devices in a multi-layer evaporator. The liquid phase stream a and the gas phase stream B which flow in parallel from the upper structure enter the gas-liquid separation device 9 first. The gas-liquid separation plant has a plurality of submerged pipelines, wherein the central liquid phase submerged pipeline 19 is inserted into the liquid to a greater depth than the plurality of gas phase submerged pipelines 18 dispersed around, so that the gas phase stream B automatically enters the liquid phase fluid collected in the vertical trough body 7 through the plurality of gas phase submerged pipelines 18 around to bubble, and the liquid phase stream a enters the bottom central area of the vertical trough body through the liquid phase submerged pipeline 19 under the action of gravity. The structure can not only effectively separate gas phase from liquid phase, but also make the gas phase enter a reaction system from a gas phase immersion pipeline which is uniformly distributed in a bubbling mode, and promote the mixing of the liquid phase. The liquid phase stream B stays in the vertical groove body 7 and carries out condensation polymerization reaction. As the reaction mass is continuously injected, the liquid phase stream B in the vertical trough body overflows from the overflow weir 8at the periphery and flows along the outer wall of the vertical trough body onto the tray 6B inclined towards the inlet 22 of the tubular pressure reduction unit. The gas phase B bubbling out of the liquid phase in the evaporator 10 also passes through the vertical trough 7 and the annular space of the inner wall of the reactor into the gas phase space above the tray 6B. Under the action of gravity and the gas phase pressure, the liquid phase stream A and the gas phase stream B are mixed again and enter the tubular pressure reduction unit 11.

Fig. 3a and 3b show two variants of vapor/liquid separation device 9 in a multi-layer evaporator 10, as shown in fig. 3a, in which the lengths of the 8 gas-phase immersion lines 18 directed differently are uniform. The 8 gas phase immersion lines 18 shown in figure 3b are of different lengths and are arranged in alternate long and short lengths. Due to the difference of the positions of the outlets of the gas phase pipelines of the two gas-liquid separation devices, the bubbling effect of gas on the reaction liquid phase is different so as to adapt to the change of the properties of the reaction materials.

Fig. 4a and 4b show two embodiments of the pressure reduction unit. The snakelike decompression pipe 11 comprises the diameter along with the crooked pipeline of tube side crescent, and snakelike decompression pipe 11 outside parcel has heat exchange jacket 24 to guarantee the temperature of reaction material. The gas-liquid mixture from the upper evaporator 10 enters the serpentine pressure reduction pipe 11, the system pressure is rapidly reduced along with the increase of the pipe pass, the small molecular components are rapidly evaporated to consume a large amount of heat, and meanwhile, the liquid phase reactant is continuously sticky. The serpentine shaped pressure reduction duct 11 provides two different embodiment variations, depending on the mounting, with the serpentine shaped pressure reduction duct 11 in fig. 4a being in a vertical arrangement and the serpentine shaped pressure reduction duct 11 in fig. 4b being in a horizontal arrangement.

Example 1

A nylon 66 saline solution with the temperature of 215 ℃ and the concentration of 69 percent is injected into the tower type multistage reactor, the temperature of a first layer evaporator in the first stage of the reaction is controlled at 216 ℃ and the pressure is 20 atm. The gas phase stream and the liquid phase stream pass through 3 groups of evaporators and decompression units, the operation temperature is gradually increased to 238 ℃, and the pressure is reduced to 12.6 atm. The reaction mass is injected into the second stage to continue the reaction, the second stage consists of 2 groups of evaporators and decompression units, the operation temperature is gradually increased from 238 ℃ to 280 ℃, and the operation pressure is reduced to 1 atm. The rectifying device adopts plate type rectifying tower equipment, the reflux ratio of condensed water at the top of the tower is 0.16, and the recovered hexamethylene diamine material is evenly distributed to the second stage of the reaction.

The reaction residence time of the whole tower is controlled to be 60min, and finally the nylon 66 melt material with the polymerization degree of 47 is obtained.

Example 2

A60% strength nylon 66 salt aqueous solution at a temperature of 200 ℃ was fed into a tower-type multistage reactor, and the temperature of the first-stage evaporator in the first stage of the reaction was controlled at 216 ℃ and the pressure at 18 atm. The gas phase stream and the liquid phase stream pass through 2 groups of evaporators and pressure reduction units, the operation temperature is gradually increased to 232 ℃, and the pressure is reduced to 14 atm. The reaction mass is injected into the second stage to continue the reaction, the second stage consists of 2 groups of evaporators and decompression units, the operation temperature is gradually increased from 238 ℃ to 260 ℃, and the operation pressure is reduced to 6 atm. The rectifying device adopts plate-type rectifying tower equipment, the reflux ratio of condensed water at the top of the tower is 0.16, and the recycled hexamethylene diamine material is 2: a ratio of 1 was injected on each of the two trays of the second stage. The reaction residence time of the whole tower is controlled to be 55min, and finally the nylon 66 melt material with the polymerization degree of 37 is obtained.

Claims

1. A vertical multi-stage reactor comprises a plurality of reaction layers; the top of the reactor is provided with a liquid phase inlet (1) and a gas phase inlet (2), and the bottom of the reactor is provided with an outlet (5);

each reaction layer comprises an evaporator (10) and a tubular pressure reduction unit, the evaporator (10) comprises a tank body (7) and a first tower tray (6 a) positioned above the tank body (7), an outlet of the first tower tray (6 a) is positioned above the tank body (7), and the tank body (7) is provided with a heat supply coil pipe (20);

the tubular pressure reduction unit comprises a snake-shaped pressure reduction pipe (11) and a second tray (6 b) positioned above the snake-shaped pressure reduction pipe (11), an outlet of the second tray (6 b) is connected with the snake-shaped pressure reduction pipe (11), and a heat exchange jacket (24) is coated on the outer side of the snake-shaped pressure reduction pipe (11); the edges of the first tray (6 a) and the second tray (6 b) are hermetically connected with the wall of the reactor; liquid phase substances and gas phase substances firstly enter a groove body (7) through an outlet of a first tray (6 a); the liquid and the gas overflowing from the tank body (7) flow downwards from a gap between the tank body (7) and the wall of the reactor, enter the serpentine pressure reducing pipe (11) through an outlet of the second tray (6 b), and flow into the first tray (6 a) of the next reaction layer;

all the reaction layers except the first reaction layer are provided with gas phase outlets for discharging gas overflowing from the groove body (7);

the reaction layer is divided into a first stage reaction layer and a second stage reaction layer, the first stage reaction layer is positioned above the second stage reaction layer, wherein, in each second stage reaction layer, the edge of the first tray is provided with a liquid phase inlet, the gas discharged from the gas phase outlet is separated to obtain diamine, the diamine is input from the liquid phase inlet and flows into the first tray (6 a) of the next reaction layer together with the liquid and the gas discharged from the outlet of the serpentine decompression pipe (11) of the previous layer.

2. The reactor according to claim 1, wherein the number of the first-stage reaction layers is 2 to 12, and the number of the second-stage reaction layers is 2 to 12.

3. A reactor according to claim 1, wherein said first tray (6 a) has a funnel configuration with an inclination from edge to outlet of not more than 15 degrees.

4. A reactor according to claim 1, characterized by further comprising a gas-liquid separation device (9), the gas-liquid separation device (9) comprising a plurality of submerged lines connected at their upper ends to the first tray (6 a) and inserted at their lower ends into the tank (7), wherein the centrally located liquid submerged line (19) is inserted to a greater depth into the liquid than the plurality of peripherally dispersed gas submerged lines (18); the gas immersion lines (18) are evenly distributed circumferentially along the liquid immersion line (19).

5. Reactor according to claim 4, characterized in that the lengths of the gas-phase immersion lines (18) directed towards each other are uniform or arranged in an alternate long and short manner.

6. A process for the continuous synthesis of polyamides, comprising the use of a multistage vertical reactor according to claim 1, characterized in that it comprises: and (2) taking a solution containing polyamide salt water as a liquid phase stream, taking a gas containing inert gas, water vapor and diamine as a gas phase stream, and carrying out multistage reaction to synthesize the polyamide, wherein the flow directions of the liquid phase stream A and the gas phase stream B are the same, and the gas phase pressure of each stage of reaction is gradually reduced along the flow direction.

7. The method of claim 6, wherein the polyamide salt is selected from the group consisting of caprolactam salt, undecanolactam salt, dodecalactam salt, butanediamine adipate, pentanediamine adipate, hexanediamine sebacate, hexanediamine dodecacarbonate, decanediamine sebacate, and dodecadiamine dodecacarbonate.

8. The method according to claim 6, wherein the gas phase pressure of the first stage reaction is 20atm or less, and the gas phase pressure of the last reaction is 1atm or more.

9. The method of claim 8, wherein the gas phase pressure of the first stage reaction is 18 atm.